The proposed work attempts to quantitatively define the particular environmental stimuli which produce acute and chronic increases in systemic arterial blood pressure in rhesus monkeys. The primary hypothesis to be tested is that the degree of uncertainty demanded in a discriminated avoidance task is directly related to hypertensogenic effects. The degree of uncertainty is experimentally manipulated by varying the amount of feedback which signals a successful coping response and by introducing random negative reinforcement. Periodic measurements of cardiac output, as well as hourly recordings of systemic arterial blood pressure and pulse rate, will be made during the three month experimental period. This project aims to develop the most efficient methods to produce a laboratory model of hypertension due to environmental factors and to study some of the hemodynamic consequences of environmental stressors. BIBLIOGRAPHIC REFERENCES: Forsyth, R.P.: Effect of propranolol on stress-induced hemodynamic changes in monkeys. In: Beta-adrenoceptor Blocking Agents (eds., Saxena, P.R. and R.P. Forsyth), North-Holland, Amsterdam, pp. 317-322, 1976. Walson, P.D., J. Pesout, R.P. Forsyth, N. Castagnoli and K.L. Melmon: Hypotensive activity of S-alpha-methyldopa during long-term (steady-state) intravenous infusions. J. Pharmacokin. Biopharm. 4:389-394, 1976.